Diseases caused by elevated levels of uric acid fall into two major categories: disorders caused by precipitation of uric acid crystals and diseases related to pathological effects of soluble uric acid. Gouty arthritis is the classic example of the former. Deposition of urate crystals in the kidney is also a common cause of renal dysfunction. Elevated levels of soluble uric acid are associated with a variety of disorders, including cardiovascular and renal diseases.
Gout is most commonly manifested as inflammation of one or more of the joints in the body resulting in mild to severe pain. These events may be episodic and/or chronic. Over time gout can result in the destruction of cartilage and bone, development of uric acid crystal deposits, kidney pain and dysfunction as well as kidney stones. Gout can affect other organs as well.
Gout is caused by hyperuricemia and the consequent formation and deposition of uric acid crystals in tissues, joints, kidneys and other organs. The uric acid comes from normal cell metabolism and from some types of foods and beverages. The excessive levels of uric acid are the result of too much uric acid production, impaired clearance by the kidneys (or a combination of excess production and impaired clearance), and also by some forms of medications taken for other health conditions. (Examples include diuretics, pyrazinamide, cyclosporine, low-dose aspirin, nicotinic acid and levodopa.). Many types of health conditions can also contribute to hyperuricemia and gout, including alcoholism, leukemia, lymphoma, lung cancer, tumor-lysis syndrome, smoking, psoriasis, obesity, kidney dysfunction, congestive heart failure, starvation, anemia, high blood pressure, diabetes, immobility, Lesch-Nyhan Syndrome, Down syndrome, and thyroid and parathyroid dysfunctions.
Gout is generally divided into four categories based upon progressively more severe symptoms:                1) Asymptomatic. Elevated uric acid levels in the blood, but no overt symptoms.        2) Acute gouty arthritis: Sudden onset of symptoms, often in a single joint (commonly a big toe), and then involving other joints. Symptoms include pain, swelling, redness and fever.        3) Intercritical gout: Asymptomatic phases between gout attacks.        4) Chronic tophaceous gout: A chronic condition that may include frequent attacks, constant mild pain and inflammation of joints, destruction of cartilage and bone, development of uric acid crystal deposits, kidney dysfunction and kidney stones.        
Medications currently used to treat the acute symptoms of gout include nonsteroidal antiinflammatory drugs, colchicine and corticosteroids. All of these medications can produce mild to severe side effects. Other treatments for these acute symptoms are being studied, including antibodies and antagonists to inflammatory cytokines such as Interleukin 1.
Other types of medication are used in order to try to reduce the incidence or severity of future attacks by reducing levels of uric acid. The three principal classes of medication are xanthine oxidase inhibitors (for example, allopurinol), which reduce production of uric acid from xanthine; uricosuric agents (for example, sulfinpyrazone, probenecid, benzbromarone and losartan), which are intended to improve excretion of uric acid by inhibiting reuptake of secreted uric acid in the renal tubules via inhibition of uric acid transporter 1 (URAT1) (See also US Patent Application Publication No. 2007/0010670, published Jan. 11, 2007 (Japan Tobacco Inc.)) or other elements of uric acid reuptake; and uricases, for example a pegylated-uricase such as PURICASE (Savient's pegylated recombinant mammalian uricase). These medications also often result in significant and undesirable side effects. For example, allopurinol has been reported to cause at least 100 cases of Stevens-Johnson/Toxic Epidermal Necrolysis and approximately 30 deaths each year in Europe (Halevy et al., Allopurinol is the most common cause of Stevens-Johnson syndrome and toxic epidermal necrolysis in Europe and Israel. J Am Acad Dermatol. 58(1):25-32, 2008). Probenicid and benzbromarone have been taken off the market in a number of countries due to undesirable side effects, such as liver failure in the case of benzbromarone. Patient compliance in taking these drugs is reportedly very poor (A. A. Reidel et al. “Compliance with Allopurinol Therapy among Managed Care Enrollees with Gout: A Retrospective Analysis of Administrative Claims.” Journal of Rheumatology 2004; 31:1575-1581), presumably because of the side effects and/or lack of benefit.
More than 5 million people in the U.S. have gout (National Health and Nutrition Examination Survey 111, 1988-1994). The prevalence of hyperuricemia and gout in the U.S. in 1999 was reported to be 41 per 1,000 and 14 per 1,000 in the U.K. (T. R. Mikuls et al., “Gout Epidemiology: Results for the UK General Practice Research Database, 1990-1999.” Annals of the Rheumatic Diseases 2005; 64:267-272). Subsequent reports indicate that the prevalence in the U.S., U.K. and other countries has been climbing steadily. (K. L. Wallace et al., “Increasing Prevalence of Gout and Hyperuricemia over 10 Years Among Older Adults in a Managed Care Population.” Journal of Rheumatology 2004; 31: 1582-1587). More recent data suggest that far more than 5 million Americans now have diagnosable gout. (E. Krishnan et al., “Gout in Ambulatory Care Settings in the United States.” Journal of Rheumatology 2008; 35(3): 498-501).
Hyperuricemia and gout are particularly significant issues in organ transplant recipients (Stamp, L., et al, “Gout in solid organ transplantation: a challenging clinical problem”, Drugs (2005) 65(18): 2593-2611). Uric acid is often elevated in patients with renal transplants, and common immunosupressive drugs such as cyclosporine can cause particularly severe hyperuricemia. In transplant patients, allopurinol is contra-indicated due to interactions with some immunosupressants such as azathioprine, and due to bone marrow failure caused by the combination. Furthermore, elevated uric acid may contribute to graft failure (Armstrong, K. A. et al., “Does Uric Acid Have a Pathogenetic Role in Graft Dysfunction and Hypertension in Renal Transplant Patients?” Transplantation (2005) 80(11): 1565-1571). Therefore, there is a particularly acute need for safe agents that reduce hyperuricemia in transplant recipients.
Diseases related to elevated soluble uric acid often involve vascular problems: hypertension (Sundstrom et al., Relations of serum uric acid to longitudinal blood pressure tracking and hypertension incidence. Hypertension. 45(1):28-33, 2005), prehypertension (Syamela, S. et al., Association between serum uric acid and prehypertension among US adults. J Hypertens. 25 (8) 1583-1589, (2007), atherosclerosis (Ishizaka et al., Association between serum uric acid, metabolic syndrome, and carotid atherosclerosis in Japanese individuals. Arterioscler Thromb Vasc Biol. (5):1038-44, 2005), peripheral artery disease (Shankar, A. et al., Association between serum uric acid level and peripheral artery disease. Atherosclerosis doi 10: 1016, 2007), vascular inflammation (Zoccali et al., Uric acid and endothelial dysfunction in essential hypertension. J Am Soc Nephrol. 17(5):1466-71, 2006), heart failure (Strasak, A. M. et al., Serum uric acid and risk of cardiovascular mortality: A prospective, long-term study of 83,683 Austrian men, Clin Chem. 54 (2) 273-284, 2008; Pascual-Figal, Hyperuricaemia and long-term outcome after hospital discharge in acute heart failure patients. Eur J Heart Fail. 2006 Oct. 23; [Epub ahead of print]; Cengel, A., et al., “Serum uric Acid Levels as a Predictor of In-hospital Death in Patients Hospitalized for Decompensated Heart Failure.” Acta Cardiol. (October 2005) 60(5): 489-492), myocardial infarctions (Strasak, A. M. et al.; Bos et al., Uric acid is a risk factor for myocardial infarction and stroke: the Rotterdam study. Stroke. 2006 June; 37(6):1503-7), renal dysfunction (Cirillo et al., Uric Acid, the metabolic syndrome, and renal disease. J Am Soc Nephrol. 17(12 Suppl 3):S165-8, 2006; Z. Avram and E. Krishnan, Hyperuricemia—where nephrology meets rheumatology. Rheumatology (Oxford), 47(7): 960-964, 2008), and strokes (Bos et al., 2006). Uric acid directly causes endothelial dysfunction (Kanellis, et al., Uric acid as a mediator of endothelial dysfunction, inflammation, and vascular disease. Semin Nephrol. 25(1):39-42, 2005; Khosla et al, Hyperuricemia induces endothelial dysfunction. Kidney Int. 67(5):1739-42, 2005). In children and adolescents, early-onset essential hypertension is associated with elevated serum uric acid, and reduction of uric acid with allopurinol reduces blood pressure in these patients (Feig and Johnson, The role of uric acid in pediatric hypertension. J Ren Nutrition 17(1): 79-83, 2007; D. I. Feig et al., Effect of allopurinol on blood pressure of adolescents with newly diagnosed essential hypertension. JAMA 300(8): 924-932, 2008. Feig et al. also state that this is a new therapeutic approach but that the side effects of existing drugs to lower uric acid may limit or prevent their use. Hyperuricemia is an independent risk factor in all of these conditions.
Elevated soluble uric acid is also associated with or directly induces inflammatory responses. For example, uric acid is transported into vascular smooth muscle cells via organic acid transporters, especially the urate transporter URAT1, and then stimulates vascular smooth muscle cells to produce C-reactive protein, MCP-1 and other cytokines, thereby stimulating proliferation and other changes associated with atherosclerosis (Price et al., Human vascular smooth muscle cells express a urate transporter. J Am Soc Nephrol. 17(7):1791-5, 2006; Kang et al., Uric acid causes vascular smooth muscle cell proliferation by entering cells via a functional urate transporter. Am J Nephrol. 2005 25(5):425-33 (2005); Yamamoto et al., Allopurinol reduces neointimal hyperplasia in the carotid artery ligation model in spontaneously hypertensive rats. Hypertens. Res. 29 (11) 915-921, 2006), stimulates human mononuclear cells to produce IL-1β, IL-6 and TNF-α, causes marked increases in TNF-α when infused into mice, activates endothelial cells and platelets, and increases platelet adhesiveness (Coutinho et al., “Associations of Serum Uric Acid with Markers of Inflammation, Metabolic Syndrome, and Subclinical Coronary Atherosclerosis”, Amer. J. Hypertens. (2007) 20: 83-89; Levya, F., et al., “Uric Acid in Chronic Heart Failure: A Marker of Chronic Inflammation”, Eur. Heart J. (1998) 19(12): 1814-1822.). Uric acid has also been shown to inhibit bioavailability of endothelial nitric oxide and activate the renin-angiotensin system. (T. S. Perlstein et al., Uric acid and the state of the intrarenal renin-angiotensin system in humans. Kidney International. 66:1465-1470, 2004). Inokuchi et al. have shown that Interleukin 18 (IL-18) and other inflammatory agents reflect local inflammation associated with gout and that urate crystals accelerate activation of IL-18 (T. Inokuchi et al., Plasma IL-18 and other inflammatory cytokines in patients with gouty arthritis and monosodium urate monohydrate crystal-induced secretion of IL-18. Cytokine. 33(1): 21-27, 206), which appears to have a causative role in renal failure. IL-18 and other cytokines are also significantly elevated in people who do not have gout per se but who merely have elevated uric acid levels (C. Ruggiero et al. Uric acid and inflammatory markers. (C. Ruggiero et al., Uric acid and inflammatory markers. European Heart Journal. 27: 1174-1181, 2006).
Hyperuricemia is also associated with cognitive impairment and other forms of central nervous system dysfunction. (Schretlen, D. J. et al., “Serum Uric Acid and Cognitive Function in Community-Dwelling Older Adults”, Neuropsychology (January 2007) 21(1): 136-140; Watanabe, S., et al., “Cerebral Oxidative Stress and Mitochondrial Dysfunction in Oxonate-Induced Hyperuricemic Mice”, J. Health Science (2006) 52: 730-737).
Elevated serum uric acid levels are also associated with increased risk of cancer and cancer mortality. (Strasak, A M et al. (2007) Serum uric acid and risk of cancer mortality in a large prospective male cohort. Cancer Causes Control 18 (9) 1021-1029; Strasak, A M et al. (2007) The role of serum uric acid as an antioxidant protecting against cancer: prospective study in more than 28,000 older Austrian women. Annals Oncol 18 (11) 1893-1897; Jee, S A et al. (2004) Serum uric acid and risk of death from cancer, cardiovascular disease or all causes in men Eur. J. Cardiovascular Prev. Rehab. 11 (3) 185-191)
Elevated levels of uric acid are associated with prediabetes, insulin resistance, the development of Type 2 diabetes, and an increased probability of a variety of undesirable conditions in people with diabetes, such as peripheral artery disease, strokes, and increased mortality risk, (Ioachimescu, A. G. et al. (2007) Serum uric acid, mortality and glucose control in patients with Type 2 diabetes mellitus: a PreCIS database study Diabet. Med. 24 (12) 1369-1374; Perry, I. J. et al (1995) Prospective study of risk factors for development of non-insulin dependent diabetes in middle aged British men BMJ 310 (6979) 560-564; Chien, K-L et al. (2008) Plasma uric acid and the risk of Type 2 diabetes in a Chinese community Clin. Chem. 54 (2) 310-316; Sautin, Y. Y. et al. (2007) Adverse effects of the classic antioxidant uric acid in adipocytes: NADPH oxidase-mediated oxidative/nitrosative stress Am. J. Physiol. Cell Physiol. 293: C584-0596; Tseng, C. H. (2004) Independent association of uric acid levels with peripheral artery disease in Taiwanese patients with Type 2 diabetes Diabet. Med. 21 (7) 724-729; Lehto, S. et al. (1998) Serum uric acid is a strong predictor of stroke in patients with non-insulin dependent diabetes mellitus Stroke 29: 635-639.)
Elevated levels of uric acid are a defining feature of Lesch-Nyhan Syndrome. People with sleep apnea or sleep-disordered breathing also have elevated of uric acid (Saito, H. et al., Tissue hypoxia in sleep apnea syndrome assessed by uric acid and adenosine. Chest 122: 1686-1694, 2002; Verhulst, S. L., et al., Sleep-disordered breathing and uric acid in overweight and obese children and adolescents. Chest 132: 76-80, 2007)
Elevated uric acid is associated with preeclampsia (Bainbridge, S. A. and Roberts, J. M., Uric acid as a pathogenic factor in preeclampsia. Placenta Dec. 17, 2007 epub ahead of print).
“Uric acid is a major contributor of the inflammatory response triggered by P. falciparum in human peripheral blood mononuclear cells . . . . [T]he inflammatory reaction induced by P. falciparum is considered a major cause of malaria pathogenesis . . . .” PLoS ONE 2009; 4(4):e5194. Epub 2009 Apr. 17.
There is a significant medical need for new medications that can safely, conveniently and effectively treat and prevent disorders related to elevation of blood uric acid, whether such diseases are due to crystallization of uric acid or to effects of supranormal (whether by an individual or a population-based standard) levels of soluble uric acid.